Separated from the mainland by the English Channel and surrounded by potentially hostile territory, the Calais Pale relied upon constant supplies of food, clothing and building materials to maintain its viability as a military frontier. Moreover, the garrison needed to be paid and the difficulties of providing the necessary cash to meet the costs of the defence of Calais remained a constant problem for English governments between 1436 and 1558. Their success in tackling the related problems of finance and supply has been a recurrent theme in discussions of Calais under English rule. Central to the problems of finance was the relationship between the crown and the merchants of the staple, the company of merchants granted a monopoly of English wool exports to the markets of the Low Countries through Calais. The costs of the defence of Calais were met by the profits of the English wool trade; indeed, the decision to move the wool staple to Calais in Edward III's reign was governed by the need to pay for the newly acquired Pale and was greeted by protests from the English merchant community. As will become clear, the defence of Calais was, on the whole, paid for by a successful partnership between the crown and the staplers; only in periods of political crisis did this system come under strain. The decline of the wool export trade in the early sixteenth century forced a reappraisal of the way in which the crown met the costs of the defence of Calais.